Minimizing power consumption is an important key issue for mobile wireless network devices, such as laptop computers, personal digital assistant devices, etc., that are battery-powered. This issue is especially important when multimedia services are provided over the wireless network, since multimedia services are generally data-intensive and continuous. The power consumption of a wireless device comprises computational power for generating the data to be transmitted, and transmission power for sending the data wirelessly. The computational power is typically determined by computational costs for source coding and channel coding. How much power should be spent on transmission and source and channel coding calculations is closely related to another key issue for wireless communications in a system with wireless mobile devices, which is the need to satisfy different quality-of-service (QoS) requirements, such as minimum transmission rates, maximum tolerable delay, maximum tolerable distortion, etc.
Power control and joint source-channel coding (JSCC) are two effective approaches for supporting quality-of-service requirements for wireless communications, especially when the communications involve the transmission of multimedia data. Power control is performed from a group point of view by controlling transmission power and spreading gain (transmission rate) of the wireless devices in the group. Most power control schemes are designed to achieve goals such as guaranteeing the low bound of signal-to-interference ratio (SIR), balancing received power levels, or maximizing cell capacities. On the other hand, joint source-channel coding is performed by individual mobile devices by introducing redundancy through channel coding to combat transmission errors. Most existing JSCC schemes are designed to minimize data distortion. To date, the techniques of power control and JSCC have been studied separately, and few of them are concerned with the power consumption of mobile devices.
Accordingly, it is desirable to provide an effective scheme for a wireless system that minimizes the power consumption of individual wireless mobile devices while maintaining desired quality of services of the wireless communications.